NETWORK SOLUTION FROM GSM to LTE

Transcription

1 NETWORK SOLUTION FROM GSM to LTE Eng. Marim A. Emsaed Tripoli University, Faculty of Information Technology, Computer Science Department, Prof. Amer R. Zerek Zawia University, Faculty of Engineering/ EE Department, Zawia, Libya, Eng. Fareda A. Elmaryami Zawia University, Faculty of Engineering/ EE Department Zawia, Libya Abstract- LTE s study phase began in late The overall goal was to select technology that would keep 3GPP s Universal Mobile Telecommunications System (UMTS) at the forefront of mobile wireless well into the next decade. Key project objectives were set in the following areas: peak data throughput; spectral efficiency; flexible channel bandwidths; latency; device complexity; and overall system cost. The main decision was whether to pursue the objectives by continuing to evolve the existing W-CDMA air interface (which incorporates HSPA (highspeed packet access) or adopt a new air interface based on OFDM. Index Terms The motivation for LTE, OFDM, LTE access network I. INTRODUCTION LTE (both radio and core network evolution) is now on the myti5u7arket. Release 8 was frozen in December 2008 and this has been the basis for the first wave of LTE equipment. LTE specifications are very stable, with the added benefit of enhancements hatu6jving been introduced in all subsequent 3GPP Releases The motivation for LTE [4] Need to ensure the continuity of competitiveness of the 3G system for the future User demand for higher data rates and quality of Service Packet Switch optimized system Continued demand for cost reduction (CAPEX and OPEX) Low complexity Avoid unnecessary fragmentation of technologies for Paired and unpaired band operation Figure 1 component of LTE GSM was developed to carry real time services, in a circuit switched manner (in blue in fig.1), and with data services only possible over a circuit switched modem connection, with very low data rates. The first step towards an IP based packet switched (in green in fig.1) solution was made with the evolution of GSM to GPRS, using the same air interface and access method, TDMA (Time Division Multiple Access). [9] To reach higher data rates and data volume UMTS was developed with a new access network, based on CDMA (Code Division Multiple Access). The access network in UMTS emulates a circuit switched connection for real time services and a packet switched connection for data com services (in black in fig.1). In UMTS the IP address is allocated to the UE when a data com service is established and released when the service is released. Incoming data com services are therefore Still relying upon the circuit switched core for paging. LTE or the E-UTRAN (Evolved Universal Terrestrial Access Network) is the access part of the requirements for the new access network are high spectral efficiency, high peak data rates, short round trip time and frequency flexibility. The Evolved Packet System (EPS) is purely IP based. Both real time services and data com services will be carried by the IP protocol. The IP address is allocated when the mobile is switched on and released when switched off [3]. 110

2 The new access solution, LTE, is based on OFDMA (Orthogonal Frequency Division Multiple Access) to be able to reach even higher data rates and data volumes. High order modulation (up to 64QAM), large bandwidth (up to 20 MHz) and MIMO transmission in the downlink (up to 4x4) is also a part of the solution. The highest theoretical data rate is 170 Mbps in uplink and with MIMO the rate can be as high as. Other access technologies not developed by 3GPP, like WiMAX and WiFi. Non 3GPP developed access solutions are divided in trusted and non-trusted. This division is not based on the technical solution but the business relation/agreement between the operators The core network EPC is prepared to work with other access technologies not developed by 3GPP, like WiMAX and WiFi. Non 3GPP developed access solutions are divided in trusted and non-trusted. This division is not based on the technical solution but the business relation/agreement between the operators The LTE access network is simply a network of base stations, evolved Node (enb), generating a flat architecture (figure 1). There is no centralized intelligent controller, and the enbs are normally Figure 2 towards the core network by the S1-interface Inter-connected by the X2-interface and towards the core network by the S1-interface (figure 2).. The reason for distributing the intelligence amongst the base-stations in LTE is to speed up the connection set-up and reduce the time required for a handover. For an end-user the connection set up time for a real time data session is in many cases crucial, especially in on-line gaming. The time for a handover is essential for real-time services where end-users tend to end calls if the handover takes too long. Another advantage with the distributed solution is that the MAC protocol layer, which is responsible for scheduling, is represented only in the UE and in the base station leading to fast communication and decisions between the enb and the UE. In UMTS the MAC protocol, and scheduling, is located [7] the controller and when HSDPA was introduced an additional MAC sub-layer, responsible for HSPA scheduling was added in the NB. The scheduler is a key component for the achievement of a fast adjusted and efficiently utilized radio resource. The Transmission Time Interval (TTI) is set to only 1 ms. During each TTI the enb scheduler shall consider the physical radio environment per UE. The UEs report their perceived radio quality, as an input to the scheduler to decide which Modulation and Coding scheme to use. The solution relies on rapid adaptation to channel variations, employing HARQ (Hybrid Automatic Repeat Request) with softcombining and rate adaptation [1] Prioritize the QoS service requirements amongst the UEs. LTE supports both delay sensitive real-time services as well as data com services requiring high data peak rates. To schedule a low data rate, real-time service leads to a pleased customer but a low utilized radio spectrum. Inform the UEs of allocated radio resources. The enb schedules the UEs both on the downlink and on the uplink. For each UE scheduled in a TTI there will be a Transport Block (TB) generated carrying user data. In DL there can be a maximum of two TBs generated per UE if MIMO is used. The TB will be delivered on a transport channel. In LTE the number of channels is decreased compare to UMTS. For the user plane there is only one shared channel in each direction. The TB sent on the channel, can therefore contain bits from a number of services, multiplexed together. In theory the highest number of users that can be scheduled during 1 ms is 440, presuming 20 MHz band and 4x4 Multi User MIMO. To achieve high radio spectral efficiency a multicarrier approach for multiple access was chosen by 3GPP. For the downlink, OFDMA (Orthogonal Frequency Division Multiple Access) was selected and for the uplink SC-FDMA (Single Carrier - Frequency Division Multiple Access) also known as DFT (Discrete Fourier Transform) spread OFDMA (figure 3). Figure 3 radio spectral efficiency a multicarrier approach for multiple access

3 OFDM is a multicarrier technology subdividing the available bandwidth into a multitude of mutual orthogonal narrowband subcarriers. In OFDMA these subcarriers can be shared between multiple users. This solution is achieving very high spectral efficiency, but requires fast processors. It makes it possible to exploit variations in both frequency and time domains. The OFDMA solution leads to high peak-toaverage power ratio requiring expensive power amplifiers with high requirements on linearity, increasing the battery consumption. This is no problem in the enb, but would lead to very expensive handsets. Hence a different solution with lower requirement on the handset was selected for the UL. To enable possible deployment around the world, supporting as many regulatory requirements as possible, LTE is developed for a number of frequency bands, ranging from 800 MHz up to 3.5 GHz. The available bandwidths are also flexible starting with 1.4 MHz up to 20 MHz. LTE is developed to support both the time division duplex technology (TDD) as well as frequency division duplex (FDD).[2] Since LTE provides high spectral efficiency, supports high data rates and implements flexible access architecture, it is proven to become a success amongst operators as well as customers. Figure 5 path loss models and antenna gain patterns Throughput and BLER over time. The blue line depicts the UE throughput in Mb/s for the selected stream and UE, as well as the BLER as measured by the ACK/NACK ratio (green line) and the BLER value applied by the link quality model. Although the system is calibrated to deliver BLERs_0.1, the actual results are influenced by the uplink delay and time variability of the channel. Figure 4 read the path loss maps Graphical User Interface (GUI) that shows you the available macroscopic path loss models and antenna gain patterns. Does not actually plot results. Sector throughput and BLER: for every sector, shows the average throughput (summing both streams, when applicable) and overall BLER. If no users are assigned to the sector, NaN may be displayed as BLER. Note that all time-dependant data is averaged by using a rectangular window of configurable length Figure 6 network BLER and throughput using 5MHZ bandwidth UE position in the ROI. sent CQI report for the selected RB and stream (blue), mean CQI for the whole frequency band (red) and CQI of to the Transport Block (TB) sent to the UE, if scheduled. Distribution of the CQIs for the selected UE and RB during the simulation time (blue), and of the TB CQIs (red).

4 Figure 7 LTE-GUI-show-UE-traces GUI GUI depicting the cell traces for the selected enodeb/sector pair. Contains the following figures: Figure 8 LTE-GUI-show-cell-traces GUI Graphical depiction of the RB allocation for the selected TTI. Throughput and BLER for the selected stream number. Throughput and BLER are averaged using a rectangular window of configurable length. In order to make the postprocessing faster Evolution of the number of assigned RBs to each UE during the selected TTI range. The cell throughput is calculated with the ACKed data from the UEs instead of checking the throughput of every attached UE. Thus, the uplink delay makes you lose the value for some TTIs. These terms (license for the LTE system level simulator) refer to the use of the LTE system-level simulator (the Original Work), developed by the Institute of Communications and Radio Frequency Engineering, Vienna University of Technology (the licensor). A. Academic Usage cientifically significant Results that can be used for publication B. Grant of copyright license Licensor grants you a worldwide, royalty-free, nonexclusive, non-sublicensable license, restricted to noncommercial use, for the duration of the copyright, to install the Original work and any Academic Usage in the context of this license describes the use of the Original Work in scientific projects without any reimbursement or financial claims that bear on results derived by the Original Work, but subject however to the restrictions provided for in Clause B herein below. The main goal in the sense of Academic Usage shall be to obtain Derivative Works thereof on one personal computer. The license allows you to: 1) Use the Original Work only for Academic Usage. Any usage of the Original Work, entirely or in part or modified, requires the proper citation, e.g. as reference in a publication. 2) Translate, adapt, alter, transform, modify, or arrange the Original Work, thereby creating derivative works ( Derivative Works ) based upon the Original Work. Distribution, either royalty-free or commercially, in parts or in modified form of the Original Work, i.e. also of Derivative Works, is prohibited and not covered by "Academic Usage. 3) Display results derived from the Original Work, or in be used without express prior permission of the Licensor except as expressly provided otherwise in Clause B1 hereinabove. Except as expressly stated herein, nothing in this License grants any license to Licensor s trademarks, copyrights, patents, trade secrets or any other intellectual property. No license is granted to the trademarks of Licensor even if such marks are included in the Original Work Nothing in this License shall be interpreted to prohibit modified form, publicly, without commercial usage. C. Grant of source code license The term Source Code means the preferred form of the Original Work for making modifications to it and all available documentation describing how to modify the Original Work. Licensor agrees to provide a machine-readable copy of the Source Code of the Original Work along with each copy of the Original Work that Licensor distributes. Licensor reserves the right to satisfy this obligation by placing a machine-readable copy of the Source Code in an information repository reasonably calculated to permit inexpensive and convenient access by you for as long as Licensor continues to distribute the Original Work.

5 D. Neither the names of Licensor, nor the names of any contributors to the Original Work, nor any of their trademarks or service marks, may Licensor from licensing under terms different from this License any Original Work that Licensor otherwise would have a right to license. E. Warranty of provenance and disclaimer of warranty Licensor warrants that the copyright in and to the Original Work is owned by the Licensor or is sublicensed to You under the terms of this License with the permission of the contributor(s) of those copyrights and patent rights. Except as expressly stated in the immediately preceding sentence, the Original Work is provided under this License on an "AS IS" BASIS and WITHOUT WARRANTY, either express or implied, including, without limitation, the warranties of noniinfringement, merchantability or fitness for a particular purpose. THE ENTIRE RISK AS TO THE QUALITY OF THE ORIGINAL WORK IS WITH YOU. [5] P. Viswanath, D. Tse, and R. Laroia, Opportunistic beamforming using dumb antennas, IEEE Transactions on Information Theory, vol. 48, pp , [6] Technical Specification Group Radio Access Network, Evolved universal terrestrial radio access (E-UTRA); LTE radio frequency (RF) system scenarios, 3rd Generation Partnership Project (3GPP), Tech. Rep. TS , [7] Physical layer aspects for evolved universal terrestrial radio access (UTRA), 3rd Generation Partnership Project (3GPP), Tech. Rep. TS ,2006. [8] H. Claussen, Efficient modelling of channel maps with correlated shadow fading in mobile radio systems, Sept [9] Recommendation ITU-R M.1225: Guidelines for evaluation of radio transmission technologies for IMT-2000, Tech. Rep., F. Limitation of liability Under no circumstances and under no legal theory, whether in tort (including negligence), contract, or otherwise, shall the Licensor be liable to anyone for any indirect, special, incidental, or consequential damages of any character arising as a result of this License or the use of the Original Work including, without limitation, damages for loss of goodwill, work stoppage,[8] computer failure or malfunction, or any and all other commercial damages or losses. This limitation of liability shall not apply to the extent applicable law prohibits such limitation. G. Termination If, at any time, you infringe upon the grants of this License, it shall terminate immediately and you may no longer exercise any of the rights granted to you by this License REFERENCES [1] [2] J. C. Ikuno, M. Wrulich, and M. Rupp, System level simulation of LTE networks, in Proc IEEE 71st Vehicular Technology Conference, Taipei,Taiwan, May [3] Technical Specification Group Radio Access Network, Evolved universal terrestrial radio access (E-UTRA); physical channels and modulation, 3rd Generation Partnership Project (3GPP), Tech. Rep. TS Version 8.7.0, May [4] Random number stream - MATLAB. [Online]. Available: ef/randstream.randstream.html